Short-Term Borrowings - Summary of Short-Term Borrowings and Weighted-Average Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Short-term Debt [Line Items]
Federal funds purchased	$ 193	$ 180
Other short-term borrowings	2,861	4,838
Federal Funds Purchased
Short-term Debt [Line Items]
Short-term borrowings, average	307	381
Short-term borrowings, maximum month-end balance	$ 1,143	$ 1,312
Short-term borrowings, rate	5.31%	4.22%
Short-term borrowings, average rate	4.96%	1.69%
Other Short Term Borrowings
Short-term Debt [Line Items]
Short-term borrowings, average	$ 5,044	$ 4,544
Short-term borrowings, maximum month-end balance	$ 7,423	$ 8,606
Short-term borrowings, rate	5.21%	3.75%
Short-term borrowings, average rate	4.90%	2.39%